Addition of urea to viscose



Juan

Patented Aug. 11, 1953.

UNITED STATES PATENT OFFICE Gergxzi j il ift fj i izgz g fia assignor toAmerican Viscoseflorporation, Wilmington, Del-., a corporation" ofDelaware No Drawing. Ap iidatimj yo ember 19,1947, Serial No. 787,023"

30laims. (o1. 166L165)" This-invention relates to fibers and yarns com--prising regenerated cellulose characterized by high breaking toughnessand low average"stifi-- ness, and to the production of such fibers andyarns from viscose;

Breaking toughness is defined as the work required to break a givenyarn, and has the dimensions gram centimeters per denier centimeter. Itis numerically equal to the area under the stress-strain curve obtainedfrom various tensile strength testing machines. Average stiffness is ameasure of the extensibility of the yarns at a given load and isnumerically equal to the ratio of-thetensile strength at break, to theelongation at break. The terms breaking toughness and average stiffnessare explained in detail in the paper by Harold De Witt Smith, publishedin the Proceedings of the American Society for Testing Materials, vol.44, 1944, pp. 589-90.

In the past, the production of fibers and yarns from viscose having thecombined characteristics of high breaking toughness, and lowaverage'stiffness, has invariably involved changes in' the compositionand salt test of the Viscose, as Well as in the spinning conditions, ascompared to the Viscoses and spinning conditions normally used 'for'the.production of fibers and yarns.

The object of the present invention is to produce fibers and yarnscharacterized by high' breaking toughness and low average stiffness fromconventional viscoses having normal so- -dium hydroxide and cellulosecontent, of normal sa1t point (as determined by the standard sodiumobtained from a normal viscose of the same sodium hydroxide andcellulose content and salt point, and under the same spinningconditions, but in the absence of urea admixed withthevis cose.

The effective amounts of urea are in the range of from about 1 to 5%,based on the weight of the viscose.

Any normal viscose may be'used. Such normal- 'viscose" have a sodiumhydroxide content of from 6 to '8%,-based'on thewei'ght of the viscose,cellulose contentof from 6 to 8%, based on the weightof the viscose, andsalt points in the range or frame to 6.

The mixture comprisingviscose and from about 1' to5%' of urea by weightmay be spun into adueo'u's' acid spinning baths containing from about8to'l2% sulfuric acid, from about 2 to 5% zinc sulfate, and from about 16to 20% sodium sulfate; the baths being maintained at normal temperaturesof from about 55 C.

In all instances, the ureaexerts a marked effect upon the breakingtoughness and average stiffness' 'o'f the fibers and yarns obtained.However, in generaLthe effects of'the urea are more noticeable in thecase'of viscoses having the lower salt points in the range of 3 to 6stated. The lower the'saltpoint (i. e. the more highly ripene'd or agedthe viscose) the greater the increase in the breaking toughness, and thegreater the decrease in average stifiness of the fibers an'dyarnsobtained, v i

The urea may be added at any stage in the course of the viscoseproduction, but preferably the1ur'eais admixed with the viscoseimmediately after its p'roduction and prior to storage thereof forripening', during storage of the viscose for ripening," on after theviscose has been ripened and immediately prior to spinning the fibers oryarns. The urea does not substantially efi'ect the saltpoint' of theviscose, or the processes which normally take place during ripeningthereof.

The following specific examples will serve to illustrate the invention.In carrying out the processes of the'examples, the stress-strain curvementioned bySmith' (supra) was obtained by means of theScottinclinedplane tensile strength testing machine which is described in detail inthe'arti'cleby'A. Stuart Hunter, entitled Importanceof Uniformity in theConstant Rate of Loading'iwith the Scott Inclined Plane Serigraph,American'isilkand Rayon Journal, January 1937.

Example 1 About2.5% of ureawas added, with stirring, toarviscosecontaining'about 7.8% sodium hydroxide'andr'about' 7.5% ofcellulose, by weight,-'

denier yarn wh'ich 'was 'g-iven a godet stretch of 1 Qn testing," theyarn was found to have a dry breaking toughness of"51.9 gJcm/d. cm. and

average stiffness of 23.2, wet breaking toughness of 28 g. cm./d. cm.and wet average stiffness of 13.6. This compared with a dry breakingtoughness of only 38.8 g. cm./d. cm. and average stiflness of 27.2; wetbreaking toughness of 20.9 g. -cm./ d. cm., and wet average stiffness of21.5 for a yarn spun from a viscose of the same composition, under thesame conditions, but which did not contain urea.

Emample 2 To a viscose containing 7.8% sodium hydroxide and 7.5%cellulose, and having a salt point of 5.9, there was added 1.25% of,urea by weight. The viscose was then spun into an aqueous bathcontaining about 11% sulfuric acid, about zinc sulfate, and about sodiumsulfate, to produce a 150 denier, filament yarn, which was given a godetstretch of about 69%. The yarn was after-treated in the usual manner,and dried, after which it was tested for breaking toughness and averagestiffness. It was found to have a dry breaking toughness of 51.8 g.cm./d. cm., and average stiffnes of 17.0; wet breaking toughness of 37.7g. cm./d. cm., and wet average stiffness of 9.5. A similar yarn,produced from a viscose of the same salt point and basic composition,but not containing urea, was found to have a dry breaking toughness ofonly 47.8 g.

cm./d, cm. and average stiffness of 18.7, and wet breaking toughness of32.3 g. cm./d. cm. and average stiffness of 9.9.

Example 3 About 2.5% of urea was added, with stirring, to a viscosecontaining about 7.8% sodium hydroxide and about 7.5% cellulose, byweight, and having a salt point of 5.1. The viscose was then spun intoan aqueous bath containing about 10.6% sulfuric acid, about 3% zincsulfate and about 18% sodium sulfate to produce a 40 filament, 150denier yarn which was given a godet stretch of 53%. On testing, the yarnwas found to have a dry breaking toughness of 54.4 g. cm./d. cm., andaverage stiffness of 11.2; wet breaking toughness of 45.7 g. cm./ d.cm., and wet average stiffness of 5.2. This compared with a dry breakingtoughness of 48.8 g. cm./d. cm., and average stiffness of 12.6; wetbreaking toughness of 34.7 g. cm./d. cm. and Wet average stiifness of5.7 for a yarn spun from the same viscose, under the same conditions,but in the absence of urea.

Example 4 A yarn was produced from a viscose as described in Example 3,containing 2.5% urea by weight. The spinning conditions were the same asin Example 3 except that the yarn was given a godet stretch of 73%. Theyarn had a dry breaking toughness of 51 g. cm./d. cm. and averagestiffness of 17.5; wet breaking toughness of 36.1 g. cm./d. cm. and Wetaverage stifiness of 9.5, as compared to a dry breaking toughness of37.7 g. cm./ d. cm. and average stiffness of 20.6, and wet breakintoughness of 24.2 g. cm./d. cm. and wet average stiffness of 11.5, for ayarn produced under the same conditions, from a viscose of the samecellulose and sodium hydroxide content, but not containing urea.

7.3% cellulose, and having a salt point of 5.4. The viscose having theurea admixed with it was then spun into an aqueous bath containing about11.1% sulfuric acid, about 4.8% zinc sulfate, and about 19.8% sodiumsulfate, to produce a 40 filament, denier yarn which was given a stretchof about 44% between godets. This yarn had a dry breaking toughnes of48.1 g. cm./d. cm. and average stiffness of 10.4; wet breaking toughnessof 40.3 g. cm./d. cm. and wet average stiffness of 4.9. A similar yarn,from a viscose of the same sodium hydroxide and cellulose content, andof the same salt point, obtained under the same conditions, but in theabsence of urea admixed with the viscose, had a dry breaking toughnessof only 45 g. cm./d. cm. and average stiffness of 13.5; wet breakingtoughness of 33.6 g. cm./d. cm. and wet average stiffness of 5.9.

Example 6 5% of urea was added with stirring to a vis cose containingabout 7.5% sodium hydroxide: and about 7.6% cellulose, and having a saltpoint of 5.4. The viscose was then spun into an aque-- ous bathcontaining about 10.9% sulfuric acid, about 4.7% zinc sulfate, and about20% sodium. sulfate, to produce a 40 filament, 150 denier yam which wasgiven a godet stretch of about 65%.. The yarn was then after-treated anddried in the usual way. The dried yarn had a dry breaking: toughness of51.4 g. cm./d. cm. and average stiffness of only 14.9; wet breakingtoughness of 32.2; g. cm./d. cm. and wet average stiffness of 4.9.. Yarnobtained from a viscose of the same fundamental composition but whichdid not contain'. urea was found to have a dry breaking tough-- ness ofonly 44.4 g. cm. /d. cm. and average stiffness as high as 18.8; wetbreaking toughness of" 25.5 g. cm./d. cm. and wet average stiffness. of9.8.

As is apparent from the foregoing examples;

the fibers and yarn spun in accordance with the. conventional wetspinning technique from a viscose containing the indicated small amountsof urea are distinguished by increased breaking? toughness and decreasedaverage stiffness by vir-- tue of which they are especially welladapted; to use in which they are subjected to severe: stresses andstrains, such as the flexing to which: yarns comprising tire cords areexposed. The fibers and yarns have generally increased tensile:strengths ranging from about 2.7 to 3 gms/denier and high elongations offrom about 17 to 23%.

As has been indicated, the salt point of the viscose may be from 3 to 6,and the amount of. urea present may be from 1 to 5%. Generallyspeaking,the influence of the urea on the breaking toughness and averagestiffness of the yarns:v and fibers obtained from any given viscosecon-' taining normal amounts of cellulose and sodium. hydroxide, withinthe ranges indicated, is most?- pronounced, the lower the salt point ofthe viscose. within the stated range of 3 to 6. At salt points; of fromsay, 3 to 4, the effects of the urea on. the breaking toughness andaverage stiffness are: more pronounced even when the urea is present; inthe smaller amounts.

The urea exerts its modifying effects on the properties of the fiberseither prior to or duringtheir spinning or at any rate prior to finalsetting up of the fibers. The fibers, after their with-- drawal from thebath and after-processing in; accordance with the usual procedures,including: final washing, are found to be substantially en-- tirely freeof urea.

Since it will be obvious that changes and varia-- tions maybe madeincarrying out the invention,.

t hi 5 it will be understood that the invention is not to be limitedexcept as defined in the appended claims.

I claim:

1. A fiber-forming composition consisting of a mixture of viscosecontaining, by weight, from about 6 to about 8% of sodium hydroxide andfrom about 6 to about 8% of cellulose, and havin a sodium chloride salttest value of from 3 to 6, with from 1 to 5% by weight of urea.

2. As a fiber-forming composition, a mixture of viscose with about 1 to5% by weight of organic water-soluble material consisting of urea, theurea being the sole organic water-soluble material in the mixture, saidcomposition having normal ageing characteristics.

3. As a fiber-forming composition, a mixture of viscose containing about6 to about 8% of sodium hydroxide by weight and about 6 to about 8% byweight of cellulose, with about 1 to 5% by weight of organicwater-soluble material consisting of urea, the urea being the soleorganic water-soluble material in the mixture, the composition having-a. sodium chloride salt point oil 3 to 6.

GEORGE ALVIN RICHTER, JR.

References Cited in the file of this patent

2. AS A FIBER-FORMING COMPOSITION, A MIXTURE OF VISCOSE WITH ABOUT 1 TO5% BY WEIGHT OF ORGANIC WATER-SOLUBLE MATERIAL CONSISTING OF UREA, THEUREA BEING THE SOLE ORGANIC WATER-SOLUBLE MATERIAL IN THE MIXTURE, SAIDCOMPOSITION HAVING NORMAL AGEING CHARACTERISTICS.